Pressure swing adsorption process and apparatus

Abstract

A low pressure swing adsorption process and apparatus for the recovery of carbon dioxide from multi-component gas mixtures, utilizing the simultaneous purge and evacuation of opposite ends of the adsorber(s) to effect controlled depressurization in the adsorber bed(s) to maintain the constant purity of a carbon dioxide-enriched product stream recovered from the adsorber inlet(s).

What is claimed is:  
     
       1. A pressure swing adsorption process for the recovery of at least a heavy gas component from a multi-component gas mixture that includes said heavy gas and one or more light gas components, which comprises: 
       (1) feeding the multi-component gas mixture into an inlet of and through at least one adsorber and at an adsorption pressure, adsorbing the heavy component of the gas mixture on an adsorbent within the adsorber and removing an effluent enriched with the light component or components of the mixture from the adsorber through an outlet thereof, at least a portion of the light component-enriched effluent being retained in a pressure zone communicating with the adsorber outlet;  
       (2) blowing down a portion of the light component-enriched effluent cocurrently through the adsorber outlet into a vacuum zone maintained at a pressure less than said adsorption pressure and communicating with the adsorber and, at the same time, removing desorbed gas by countercurrent evacuation from the adsorber through the adsorber inlet, to simultaneously depressurize the adsorber cocurrently from its outlet and countercurrently from its inlet;  
       (3) terminating the flow of the blowdown gas through the adsorber outlet while continuing the countercurrent evacuation of the desorbed gas from the adsorber inlet to further depressurize the adsorber until the pressure in the adsorber is less than that in the vacuum zone;  
       (4) passing the blowdown gas as a purge gas stream from the vacuum zone to the adsorber outlet countercurrently to and through the adsorber to make and recover a product stream enriched in the heavy gas component;  
       (5) terminating the flow of the blowdown gas from the vacuum zone and passing said light component-enriched effluent from the pressure zone into the outlet of the adsorber to partially repressurize the adsorber;  
       (6) passing an additional portion of the multi-component feed gas mixture into the inlet of the adsorber to complete repressurization of the adsorber; and  
       (7) repeating the foregoing steps to produce the heavy component-containing product stream.  
     
     
       2. The pressure swing adsorption process of claim  1 , wherein said adsorption pressure is at about atmospheric pressure. 
     
     
       3. The pressure swing adsorption process of claim  1 , wherein CO 2  is the heavy gas component recovered, and nitrogen, oxygen, hydrogen, methane, carbon monoxide or other light gases are said light gas component(s) contained in the mixture from which the CO 2  is separated. 
     
     
       4. The pressure swing adsorption process of claim  3 , wherein at least one adsorbent utilized in step (2) has an adiabatic separation factor ΔCO 2 /ΔN 2  in excess of 2.0 and a dynamic CO 2  loading in excess of 0.1 mole/kg, at adsorption temperatures of from 300° to 400° K. and under adsorption operating pressures of approximately atmospheric pressure, when the CO 2  feed concentration, product concentration and desorption pressure are as set forth in FIG.  8 . 
     
     
       5. The pressure swing adsorption process of claim  3 , wherein the adsorbent is zeolite NaY or NaX (2.0). 
     
     
       6. The pressure swing adsorption process of claim  1 , wherein two or more adsorbers are used. 
     
     
       7. The pressure swing adsorption process of claim  6 , wherein portions of the multi-component gas mixture are fed in staged sequence through the respective adsorbers. 
     
     
       8. The pressure swing adsorption process of claim  7 , wherein portions of the multi-component gas mixture are fed through two adsorbers and the adsorbers are operated in sequence in accordance with the cycle shown in FIG. 2 of the drawing. 
     
     
       9. The pressure swing adsorption process of claim  6 , wherein portions of the multi-component gas mixture are simultaneously fed through the respective adsorbers and steps (2)-(7) are simultaneously carried out in each adsorber. 
     
     
       10. The pressure swing adsorption process of claim  1 , wherein at least a portion of the product stream recovered in step (4) is thereafter recycled to the inlet of the adsorber to effect cocurrent displacement of the gas mixture at the inlet and thereby increase the concentration of the heavy component at the inlet after step (1) of the process. 
     
     
       11. The pressure swing adsorption process of claim  1 , wherein the flow rate of the purge gas stream in step (4) is controlled during the product make step to provide substantially constant purity of the heavy component-containing product stream. 
     
     
       12. The pressure swing adsorption process of claim  1  wherein, after terminating the flow of blowdown gas to make the product stream in step (4), additional blowdown gas from the vacuum zone is passed into the adsorber outlet to augment countercurrent repressurization of the adsorber. 
     
     
       13. A process for the recovery of at least CO 2  from a multi-component gas mixture containing a less selectively adsorbable component or components selected from nitrogen, oxygen, hydrogen, methane and/or carbon monoxide, wherein the gas mixture is contacted in at least one adsorber containing adsorbent material selective for the adsorption of CO 2  by means of cyclic steps comprising: 
       (a) adsorption, during which the gas mixture is passed into said adsorber in contact with the adsorbent at an adsorption temperature of 300° to 400 K and under an adsorption pressure of 90 to 200 kPa, and the CO 2  is selectively adsorbed by the adsorbent;  
       (b) desorption during which the passage of the gas mixture into said adsorber is discontinued, and the pressure in said adsorber is reduced from the adsorption pressure to a lower desorption pressure to desorb the CO 2  from said adsorbent; and  
       (c) recovering a product stream from said adsorber containing the CO 2  in at least a predetermined, constant purity;  
       wherein the adsorbent has an adiabatic separation factor ΔCO 2 /ΔN 2  in excess of 2.0 and a dynamic CO 2  loading in excess of 0.1 mole/kg at said adsorption temperature and pressure, when the CO 2  feed concentration, product concentration and desorption pressure are as set forth in FIG.  8 .  
     
     
       14. The process of claim  13 , wherein said adsorber is simultaneously depressurized by the passage of streams enriched in the less selectively adsorbable component or components, cocurrently from an outlet and countercurrently from an inlet of said adsorber re-using the cocurrent depressurization stream as a purge gas stream in step (b) and recovering the CO 2 -containing product stream from said inlet of the said adsorber. 
     
     
       15. The pressure swing adsorption process of claim  14 , wherein at least a portion of the product stream recovered in step (b) is thereafter recycled to the inlet of the adsorber to effect cocurrent displacement of the gas mixture at the inlet and thereby increase the concentration of said CO 2  at the inlet after step (a) of the process. 
     
     
       16. The process of claim  13 , wherein the adsorbent is zeolite NaY or NaX (2.0). 
     
     
       17. An apparatus for carrying out a pressure swing adsorption process for the recovery of a heavy gas component in a multi-component gas mixture containing said heavy gas component and at least one light component, which comprises: 
       (1) at least one adsorber having an inlet end and an outlet end and incorporating at least one layer of an adsorbent capable of selectively adsorbing the heavy component of the gas mixture relative to said at least one light component thereof;  
       (2) a feed blower communicating with the inlet end of the adsorber for feeding the gas mixture into and through the adsorber;  
       (3) a pressure tank communicating with the outlet end of the adsorber for receiving a light component-enriched effluent from the adsorber and for feeding the light component-enriched effluent into the outlet end of the adsorber;  
       (4) a vacuum tank communicating with the outlet end of the adsorber for receiving a further portion of the light component-enriched effluent from the adsorber and for feeding the light component-enriched effluent as a blowdown gas in the adsorber through its outlet end;  
       (5) outlet valve means for selectively placing the pressure and vacuum tanks in communication with the outlet end of the adsorber for depressurizing and repressurizing the adsorber;  
       (6) a vacuum pump independent of the feed blower and communicating with the inlet end of the adsorber for removing a product stream containing the heavy component of the gas mixture at a predetermined, constant concentration;  
       (7) inlet valve means for selectively placing the feed blower and the vacuum pump in communication with the inlet end of the adsorber to facilitate feed of the gas mixture into and removal of the product stream from the inlet end of the adsorber; and  
       (8) control means for concurrently actuating the outlet valve means and the inlet valve means to facilitate feed of the light component-enriched effluent as a blowdown gas from the vacuum tank into the adsorber and removal of an evacuation stream from the adsorber, to simultaneously depressurize the adsorber cocurrently from its outlet end and countercurrently from its inlet end.  
     
     
       18. The pressure swing adsorption apparatus of claim  17 , said apparatus comprising two adsorbers, which are so connected to the pressure tank, vacuum tank and vacuum pump by said inlet and outlet valve means and control means as to sequentially adsorb and desorb the heavy gas component and thereby provide a continuous flow of product containing the predetermined concentration of said component. 
     
     
       19. The pressure swing adsorption apparatus of claim  17 , further comprising a storage tank communicating with the discharge from the vacuum pump and the inlet side of the feed blower for feeding a portion of the product stream into the inlet of the adsorber to effect cocurrent displacement of the gas mixture at the inlet. 
     
     
       20. The variable pressure swing adsorption apparatus of claim  17 , wherein the adsorbent is zeolite NaY or NaX (2.0).